1. Technical Field
The present invention relates in general to the art of protecting a-c equipment, and in particular to the art of protecting such a-c equipment from the effects of power surges. Specifically, the present invention relates to an improvement in a filter/protector network which is used to protect a-c equipment which will permit the a-c power to such loads to be turned off safely and instantaneously with respect to the attached load circuitry.
2. Description of the Prior Art
There are many applications where it is necessary to protect a-c load equipment from power surges and voltage transients which could deleteriously affect and damage such equipment. This protection is particularly important for equipment comprising high sensitive or complex multiple loads susceptible to electrical noise. Examples of such equipment are found in the computer art, the communications art as well as in many other arts.
As discussed in U.S. Pat. No. 4,675,772 issued to this inventor, and the disclosure of which is incorporated herein by reference thereto, there have been numerous types of protective networks designed in an attempt to protect such equipment from the power surges and transients. The above-referenced patent discloses a means for protecting such equipment from the effects of such power surges and transients in the power source as well as from respective spikes from both the source and the load.
It is often necessary to switch off the power to such equipment due to various reasons, such as environmental conditions existing adjacent to the load, or the like. Examples of such environmental reasons are: humidity in the area rising above a level that is safe for the operation of the equipment; air flow around the equipment falling to a level that is unacceptable; water forming beneath the equipment, or the like. Any of these conditions may result in damage to the load equipment or to undesirable results, and may require shut down of the load. There are, of course, many other reasons for interrupting the power to a load, and the above are intended to be examples only.
In the past, this interruption of power has been accomplished by means of relays or the like which incorporate switch circuitry. With such relay systems, the load input transformer is usually left open circuited.
However, since most load inputs include an inductor or a transformer, it has been found that when the power to such equipment is turned off in this manner, due to the characteristics of an inductor, a high voltage spike will be developed as the inductor attempts to keep current constant when the input switch is opened. This spike can damage the load equipment.
Another problem with presently known equipment is that in the event of a power outage, many circuits such as shunt trip breakers, or the like, drop out after power is restored. This may then expose the load to further transients in the source as it is being brought back up to power levels. This drop out may also expose the load to multiple transients, rapid and repeated on/off occurrences, and instabilities associated with the source/utility power loss event as well as a further transient as the shunt trip finally shuts down.
Still further, due to the characteristics of these systems, there may be a delay in the restoration of power to the load equipment after the source power is restored.
Thus, there is need for a means for interrupting power from a source to a load in a manner that is both quick and effective while still being safe for use in conjunction with sensitive electronic loads such as computers or the like.